On 2015-03-07 06:50 PM, Joseph Gwinn wrote:
On Sat, 07 Mar 2015 14:14:07 -0500, Brooks Harris wrote:
In the discussions I've been involved with many people argued
strenuously "we don't care about the past, only accurate date-time
going forward!". The reason I'm choosing to ignore the subject of
accurate date-times before 1972 is not that its not important, but
probably the same reason its side-stepped by NTP, PTP, POSIX, and GPS
- its just too expansive a topic to tackle in some commonly accepted
way. For date-time before 1972 you've got to switch to some other
timescale depending on the purpose at hand.
I figured it out the difference between GMD and UTC for POSIX. There
was an 81 microsecond error, At the time, most UNIX boxes kept time to
the nearest second, synchronized to a hairy wrist. There were advanced
systems that could do milliseconds, and in the 1980s a few that had
microsecond resolution, but we chained them to GPS via NTP, so the
error was multiple milliseconds, depending on everything.
Hi Joe,
I see the difficulties with UTC implementations and the questions at
ITU-R stemming from the historical and legacy misalignment of the
timekeeping mechanisms of the c language and POSIX and the UTC
specifications. Perhaps that's obvious. I'm not criticizing anybody
anywhere for this, its just the way its come about.
I think the only way the industry can eventually converge on reliable
"civil time" representation is to refine the underlying time mechanisms
in POSIX in some manner that allows a migration to a more comprehensive
UTC implementation. I think if a new new POSIX time specification were
to take shape it would add an option to the the conversation at ITU-R -
instead of simply "to kill Leap Seconds or not" they'd also have "a
viable migration path to comprehensive UTC timekeeping implementation"
to consider.
We understand the folks at POSIX have grappled with this topic in the
past and run into all sorts of difficulty. Given the current state of
affairs, do you think there's any way IEEE and POSIX could reengage this
topic?
-Brooks
Joe Gwinn
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